June 7 (Reuters) - Shares of AMC Entertainment and other "meme stocks" supported by individual traders jumped on Monday, extending a rally in social-media favorites into a third week as message boards hummed with talk about the potential to squeeze Wall Street short-sellers.
The sharp gains, however, have caught the attention of regulators at the Securities and Exchange Commission. On Monday the agency said it is looking into signs of market manipulation given the "volatility in certain stocks."
The volatility has also made it challenging for analysts to cover, with two analysts in the past week dropping coverage of GameStop, the stock that was catapulted higher in January by retail investors.
Cinema operator AMC Entertainment Holdings, which almost doubled in value again last week, was last up 21.1% at $58.00 while BlackBlerry's U.S. listing climbed 15.0% to $15.94 and put it up 56% since the start of June. Canadian cannabis producer Tilray's U.S. listing, meanwhile, surged 7.1%.
"AMC never ceases to amaze me. Just when I think that train is over, it jumps almost 10 points in the first 30 min of trading," one poster on Reddit wrote.
Shares of AMC are up more than 2,500% for the year to date as it has courted individual investors, while shares of video game retailer GameStop are up about 1,305% over the same time.
However some bearish investors retreated from bets against AMC on Friday as the stock fell 6.7% that day with short interest falling 74.5 million shares, or 14.9% of AMC's float by the end of trade Friday from 88.2 million on Thursday, according to S3 Partners.
Institutional investors are largely sitting on the sidelines as the meme-stock rally driven by individual investors continues.
These individual investors "don't need a reason. They're trying to do the same thing they did last week. It's a new week. They start over, the meme stock buyers, the wallstreetbets Reddit community," said Michael O'Rourke, chief market strategist at JonesTrading in Stamford, Connecticut.
Wall Street analysts have largely refused to increase their target prices - a sign of what they see as the fair value for a company's shares - despite the retail-investor driven rally.
Joseph Feldman, analyst at Telsey Advisory group terminated coverage of GameStop on Monday. His last rating on the stock was "underperform" and his last price target was $30, approximately 88% below where the company was trading Monday.
"We're focusing on other areas," said Feldman. "It's hard to justify where the stock is trading relative to the fundamentals."
That follows a similar decision last week by Bank of America to terminate coverage of GameStop "due to a reallocation of resources."
Data showed AMC has been the top-traded stock among clients of brokerages Fidelity and Freetrade, used heavily by amateur and individual investors playing with their own money.
On trading-focused social media site Stocktwits, message volume related to AMC - a barometer of interest in the stock - rose 6.2% on Monday. BlackBerry was at the top of the list of stocks being mentioned on wallstreetbets, according to the swaggystocks.com sentiment tracker.
An SEC spokesperson said in a statement on Monday that they continue to "monitor the market in light of the ongoing volatility in certain stocks to determine if there have been any disruptions of the market, manipulative trading, or other misconduct."
"In addition, we will act to protect retail investors if violations of federal securities laws are found,” the SEC said.
Market participants have told Reuters that some Wall Street institutional investors are ramping up complex options trades that let them bet the shares will fall while keeping a lid on potential losses if they instead gain.
Among other meme stocks headphones maker KOSS rose 12.3%.